Fluidic switch

ABSTRACT

A pneumatic air system for closing off a fluid passage with minimal leakage. A back pressure chamber downstream of the passage is pressurized to equal the pressure upstream of the passage. The back pressure chamber has a vent and a back pressure inlet with a member movable to close one or the other according to a control signal. An application of this switch is in a restrictor bleed system in a digital restrictor matrix as applied to a fluidic control loop in a digital to analog converter.

United States Patent Inventor Paul M. Blaiklock Newton, Mass. Appl. No. 834,837 Filed June 19, 1969 Patented June 15, 1971 Assignee The Foxboro Company Foxboro, Mas.

FLUIDIC SWITCH l C1lim,4 Drawing Figs.

11.8. CI. 137/82, 137/86, 137/608, 235/201 Int. Cl FlSc 3/14, G05d 3/00 Field of Search 137/82, 625.6, 625.60, 81.5; 135/201 con.

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2'7 comaa FLAPPER [56] References Cited UNITED STATES PATENTS 3,270,960 9/1966 Phillips.... 137/815 UX 3,353,559 11/1967 Phillips.... l37/625.66 3,489,180 1/1970 Filippi 137/6256 X Primary Examiner-Alan Cohan Atmrney- Lawrence H. Poeton ABSTRACT: A pneumatic air system for closing 05 a fluid passage with minimal leakage. A back pressure chamber downstream of the passage is pressurized to equal the pressure upstream of the passage. The back pressure chamber has a vent and a back pressure inlet with a member movable to close one or the other according to a control signal. An application of this switch is in a restrictor bleed system in a digital restrictor matrix as applied to a fluidic control loop in a digital to analog converter.

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AGENT FLUIDIC SWITCH This invention relates to fluidic switching in the sense of terminating, or removing an obstacle to, flow through a flow passage in a system of fluid operated instrumentation wherein fluid flows and pressures are used in situations such as measurement or control of processes, or energy, or parameters of these in which the stopping and starting of fluid flow are important operating functions, and in particular, in which providing minimal leakage when the flow is stopped, is of particular importance.

Fluidic systems are increasingly important in modern instrumentation, and the manipulation of pressures and flows goes to the essence of the operation of such systems. Fluidic switches and their operation are accordingly concerns of signiflcant magnitude.

It is particularly important, when flow is switched off, to provide minimal leakage. It is often important to provide essentially zero flow when a switch is operated. This is of concern in dealing with flows of ordinary magnitude, and is even more critical in the modern low flow trend toward fluidic systems in miniaturization. In such situations, even small leakage can be effect substantial error.

Of particular interest to this invention are fluidic systems of bleed to atmosphere from a fluidic control loop and through a restrictor, wherein on-off of such bleed is related to digital z'ero -one conditions.

The basis of this invention lies in the matching of an up stream pressure with a downstream pressure to establish minimal flow between these pressure situations where, as in most "cases, there remains a vestigial leakage, such leakage is supplied from a back pressure source without drawing flow through the system between such upstream and downstream pressure equalization.

As a vehicle of illustration, this invention is set forth herein as applied to a digital to analog converter system of pneumatics, in which a control loop maintains a constant pressure in a manifold, from which pneumatic bleeds are established in response to a digital input pattern as applied to fluidic switches according to this invention, in a matrix of pneumatic restrictor systems. The control, in maintaining the manifold pressure, produces an analog output signal representative of the digital input signal.

In this converter system, to achieve the digital-on-off conditions, it is necessary when the bleed flow is switched off, to terminate such flow, that the bleed flow in fact be minimal through the bleed restrictor, at essentially zero flow. Leakage downstream of the fluid switch may occur, and is compensated for by a renewal supply, in this case a regulated set point pressure without drawing flow through the bleed restrictor.

It is therefore an object of this invention to provide a fluidic switching system in which fluid flow through a passage is terminated by equalizing upstream and downstream pressures.

Other objects and advantages of this invention will be in part apparent and in part pointed out hereinafter and in the accompanying drawings, wherein:

FIG. 1 is an electrically controlled fluidic switch system according to this invention;

FIG. 2 is a pneumatically controlled fluidic switch system according to this invention; 7

FIG. 3 is a mechanically controlled fluidic switch system according to this invention; and

FIG. 4 is a schematic illustration of a fluidic digital to analog converter system embodiment switch systems according to this invention in a digital resistance input matrix.

The system of FIG. 1 is a fluidic bleed-to-atmosphere wherein a fragment of the converter system of FIG. '4 is shown. The controller has applied thereto a set point pressure as through 17 and a measurement pressure as through 16 from a supply 'manifold 15. As seen in FIG. 4, the manifold is maintained at a pressure equated to the set pressure.

The bleed system of FIG.;1 is from the manifold 15, through a fluid restrictor 26, R of FIG. 4, and through handlebars fluid switch 27 bellcrank at 25. This bleed system represents one of the digital matrix bleed systems of FIG. 4, and is illustrative of one form of all such bleed systems.

The FIG. 1 switch itself comprises a chamber 1 which receives fluid flow from the manifold 15 through the restrictor 26. A vent nozzle 2 is open to one side of the interior of chamber 1, as a vent connecting the interior of the chamber to atmosphere 25. A back. pressure supply nozzle 3 is open to the other side of the interior of chamber 1, and supply pressure thereto comes from the set point line 17 in a regulated (not shown) supply pressure equated to that in the manifold 15, but reaching the chamber 1 without passing through restrictor 26, by way of a bypass around that restrictor from the set point line to'the nozzle 3. V

The FIG. 1 switch, further, includes a metal flapper 4 internal to the chamber 1, which in one position, by its own resilient bias, rests upon and closes the back-pressure nozzle 3. An electromagnet 5 is so mounted with respect to the chamber 1 as to draw the flapper 4 away from the nozzle 3 and against the nozzle 2, when the electromagnet is energized.

Thus the fluid switch actuation, in FIG. 1, is in the form of an input electrical signal to the electromagnet 5. This switch is thus on-off, on a digital basis, as one bit of a digital input pattern as may be applied to the input of the converter system of FIG. 4.

In FIG. 1, with theelectromagnet 5 not energized, the bleed system through restrictor 26 is open and flow ensues from the manifold 15 to ground 25.- When the magnet 5 is energized, the nozzle 2 is covered by the flapper 4, and flow to atmosphere is interrupted. Because, however, there remains a residual pressure potential above atmospheric in the chamber 1, there is likely to be leakage throughthe nozzle 2 even though it is covered by the flapper 4. This would ordinarily result in bleed flow through the restrictor 26. However, the back pressure to the chamber 1 in through the nozzle 3 constantly replenishes losses from such residual bleed to atmosphere, and, by maintaining the chamber 1 pressure equal to the manifold 15 pressure, makes flow through the restrictor 26 essentially zero, and at least operationally minimal. Thus, there is minimal drain from the manifold 15, if any.

The system of FIG. 2 is like that of FIG. 1 except that the actuation of the switch 27 is pneumatic through a signal input bellows 6 as opposed by a bias bellows 7.

The system of FIG. 3 is also like that of FIG. 1 except that the actuation of the switch 27 is mechanical through a rotatable cam 8, or through other switchable mechanical means of moving the flapper 4 on the basis of a digital input signal.

FIG. 4 illustrates a digital to pneumatic analog converter, which is a combination of a digital input matrix of fluidic resistances and a pneumatic analog controller, with a manifold supply to the resistances maintained at constant pressure by the controller, and a" pneumatic analog output to a value established by the controller change necessary to maintain the manifold pressure.

This invention relates to digital to analog converters. In the FIG. 4 system, the digital input may be electrical, pneumatic or mechanical as in FIGS. 13, and the analog output is pneumatic. This is a pneumatic system to which digital input signals may be applied to switches controlling R R mR including a pneumatic controller which maintains a fixed pressure at the digital input, and has an analog pneumatic output whose pressure level is representative of the digital input signal, this pressure level being accomplished through operation of the pneumatic controller in the course of its changes as necessary to maintain the fixed pressure at the digital input.

The controller of this invention is of the nature of the disclosure in patent application to Prescott et al. Ser. No. 772,787, filed Nov. 1, 1968 and entitled Pressure Device Having Layered Construction and Pivoting Seal with Operator. The abstract of the disclosure of this patent application is as follows:

In a multilayer sandwich type of construction, an operator activated by at least one pressure chamber is brought through a sealing configuration which also provides for pivoting of the operator; the operator itself is formed from a layer of the sandwich construction and the sealing at the operator pivot is formed from scaling layers of the sandwiched construction; the operator layer may be backed by a resilient sheet layer for sealing the pressure chamber actuating the operator; this construction may be readily adapted to a plurality of pressure chambers employed in conjunction with motion-sensing devices, or alternatively weight and springs, to perform the functions of alarms, relays, repeaters, amplifiers, and a variety of other pneumatic devices.

The illustration of FIG. 4 is of an 8 bit digital to analog pneumatic converter which accepts parallel binary inputs, and transmits a 3-15 p.s.i. analog signal.

One application of this converter is in a fluidic programmer, and it is capable of accepting low level fluidic signals for such purpose. It may be used in conjunction with a punched card and pneumatic reader, to control rates, set point, or values in an analog fashion.

The system of FIG. 4 comprises a pneumatic reset controller 10, with a control loop associated therewith including an output passage 11 through a flow booster 12, past an analog output passage from the control loop at 13, through a summation resistor 14, through a supply manifold 15, and finally back to the controller as a measurement input 16, in opposition to a set point input 17 to the controller.

A digital input is generally indicated at 18, and comprises a resistance matrix to the supply manifold such that the individual flows through the individual digital resistances, for a given differential pressure, are in binary ascending ratio, as l, 2, 4, 8, ...etc.

The function of the controller 10 is to maintain the pressure in the supply manifold 15 essentially constant. The resistance matrix 18 is the recipient of digital input signals, whereas the result of the application of a digital input combination to the matrix 18 is a like combination of air bleeds to atmosphere through the specific resistances which are individual to the various units of the particular digital input combination.

The resultof each bleeding of air to atmosphere is a tendency to lowering of the pressure in the supply manifold 15. The controller 10 responds, to counteract this tendency, and the amount of this response, as necessary to achieve again a balanced condition in the control loop, is a measure of an analog output through 13, representative of the particular digital combination input signal.

The flow booster 12 provides the volume requirements of the supply manifold 15 and isolates the controller 10 from the loads produced through the digital input resistance matrix 18.

As an example of a controller 10, suitable for the system of this invention, the drawing controller illustration is a representation of one form of the previously mentioned disclosure in the patent application to Prescott et al. In this illustrative application, a proportional-reset controller form is used with pressure chambers 19, 20, 21 and 22 as measurement, setpoint, reset, and supply-bleed chambers respectively. A reset resistance-capacity system 23 and 24 is connected between the chambers 21 and 22.

Throughout the drawing, as illustration of one working ex ample, various labels as to flow and pressure are shown. These are not set forth as fixed limits or combinations, but simply as guide line values.

in the Fig. 4 resistance matrix 18, there are 8 digital bits, each one comprising an air passage from the manifold 15 to atmosphere at 25 through a resistance such as 26, with switch 27 in the passage between the resistance 26 and atmosphere at 25.

Thus, in a digital input of 0 or 1 to the switch 27 the switch 27 may be operated to open or close the passage from the manifold 15 to atmosphere, to close off that particular bit, or to bleed it off to atmosphere as the case may be.

in the showing of FIG. 4, the R bit digital input is shown as logic zero and the fluid line is open to flow from the manifold 15 to atmos here at 25, in the illustratiye input showing the R, but has a ogic one input and the fluid line 15 broken rom the manifold to atmosphere.

lclaim:

1. A fluidic switch system wherein a control system is provided with a series of individual bleed connections to atmosphere;

said switch system comprising:

a manifold in the measurement portion of said system;

a series of individual bleed lines to atmosphere from said manifold;

each of said bleed lines comprising a fluid switch and a resistor between said switch and said manifold, with said resistors provided in different restrictive capability values;

each of said switches comprising a fluid chamber continuously connected to the downstream end of its respective restrictor in terms of the flow of said bleed to atmosphere;

a nozzle exit to atmosphere from each of said chambers;

a nozzle inlet to said chamber;

a bypass of each of said restrictors to their respective nozzled inlet from the set point portion of said control system;

a nozzle closure member in each of said chambers and movable between said nozzled exit and said nozzled inlet of each such chamber to selectively close said nozzles; and

means for selectively operating said nozzle closure members to vary the bleed to atmosphere from said manifold by selectively closing said nozzled exits with the consequence of selectively terminating flow through said restrictors.

control 

1. A fluidic switch system wherein a control system is provided with a series of individual bleed connections to atmosphere; said switch system comprising: a manifold in the measurement portion of said control system; a series of individual bleed lines to atmosphere from said manifold; each of said bleed lines comprising a fluid switch and a resistor between said switch and said manifold, with said resistors provided in different restrictive capability values; each of said switches comprising a fluid chamber continuously connected to the downstream end of its respective restrictor in terms of the flow of said bleed to atmosphere; a nozzle exit to atmosphere from each of said chambers; a nozzle inlet to said chamber; a bypass of each of said restrictors to their respective nozzled inlet from the set point portion of said control system; a nozzle closure member in each of said chambers and movable between said nozzled exit and said nozzled inlet of each such chamber to selectively close said nozzles; and means for selectively operating said nozzle closure members to vary the bleed to atmosphere from said manifold by selectively closing said nozzled exits with the consequence of selectively terminating flow through said restrictors. 